Topic 6: Transfer of Heat Energy
 Convection |
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 Radiation |
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 Conduction |
Dates to Remember
October 17: Radiant energy lab due.
October 19: Convection lab due.
October 29: "Making a Transfer" presentation (p. 234):written assignment due October 30.
Nov. 1 Topic 4-6 Quiz
Final unit exam : November 13.
Radiant Energy:
Radiant energy is also called electromagnetic energy. Almost every reaction
that happen on the surface of the Earth are the result of energy coming
to the Earth from the Sun. Radiant energy is also called electromagnetic
energy because it is made up of two fields together. One of the fields
is electrical, the other is magnetic, making...electromagnetic. One
other thing to remember, when we talk about incoming radiation we don't
always mean radiation like X-rays, or radioactivity. Light is radiation
of some kind. The standard unit for radiant energy is Joule (j).
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Solar energy is the energy given off by the sun
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Solar energy is often called "radiant energy"
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Solar energy is produced by nuclear fusion reactions on the sun
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Solar energy does not pollute
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Some materials reflect solar energy
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Some materials absorb solar energy
Principles:
- Dark-colored objects absorb more heat and store more heat from sunlight than light-colored objects.
- Solar panels are usually painted black so that they will capture the most heat from the sun.
- Light-colored objects appear light to us because they are reflecting most of the light that hits them rather than absorbing it. Objects appear to be black when they absorb all wavelengths of light that hit them.
Energy Systems:
1. Energy is never created or destroyed: it is transformed from one form to another.
2. Energy transfer can be described in 5 features:
- energy source (supplies energy to system) that has the highest amount of energy
- mechanical energy e.g. wind up toy
- chemical energy e.g. gas, food
- nuclear energy e.g. sun, power plant (where splitting or fusion of particles provide energy
- direction of transfer - energy is always transferred AWAY from the source.
- transformation - energy changes from one form ot another e.g gasoline is transformed into thermal energy than causes gases to expand rapidly against a piston, transforming thermal energy to mechanical energy.
- control systems - controls on the amount of thermal energy released or transferred - e.g. home thermostats control furnace.
- waste heat - during transfer some thermal energy is lost to the surrounding area. Insulators can protect this (e.g. plastic around windows)
Making a Transfer (page 234)
Exectations:
- heat water by several degrees in 1 minutes using non-flammable materials and the heat source as a candle.
- Be able to discuss why you constructed your heat transfer system as you did.
- describe the heat source, heat transfer (radiation, convection, conduction), transformation,heat loss and control system.
- what improvments do you think you could make.
Interesting sites:
Information and definitions on radiation, convection and conduction
Radiant energy and an efficient house
Convection - transfer of heat by currents in fluids or gases.
Conduction - heat energy traveling from substance to substance or through substances using the motion of particles.
Radiation - the method of heat transfer by
waves in space